Image compression techniques have been advocated as a means to alleviate problems caused by the large volume of digital image data expected to be generated in future radiology departments. Many issues related to the use of image compression in radiology remain to be investigated. In view of the current efforts of the Joint Photographic Experts Group (JPEG) of the International Organization for Standardization (ISO) to establish a general purpose image compression standard, we believe that it is important at this time to assess the applicability of the standard algorithm to radiographic images. In this project, we are proposing to optimize the standard algorithm for the compression of digitized chest films and then to measure the dependence of diagnostic performance on the degree of compression for this optimized algorithm. The study design will enable us not only to assess differences in performance by paired comparisons, but will also define trends, if they exist, and through regression procedures will permit us to evaluate the "compression/performance" curve for this algorithm.